1. Field of the Invention
The present invention relates to a lift apparatus; and more particularly, to a lift apparatus, such as an aerial work platform, having an articulated double parallelogram boom assembly.
2. Description of Related Art
A vehicular low profile self propelled aerial work platform is disclosed in U.S. Pat. No. 4,757,875, owned by the Assignee of the instant application, wherein a work platform is mounted on the distal end of a telescopic boom assembly having its proximate end pivotally connected to a floating or riser frame assembly which, in turn, is connected to a support frame on the vehicle by a pair of parallel arms, whereby the telescopic boom assembly and associated work platform can be extended to an operative position and folded to a lowered position, so that the vehicle can be maneuvered in warehouses or manufacturing plants having nine foot high doorways.
An articulated parallelogram assembly for elevating a work platform is disclosed in U.S. Pat. No. 5,129,480, also owned by the Assignee of the instant application, wherein a lower boom assembly having parallel compression and tension arms, offset from the centerline of the vehicle, are pivotally connected between a floating or riser frame assembly and the vehicle frame. An upper boom assembly is also provided wherein parallel compression and tension arms, offset from the centerline of the vehicle, are pivotally connected between the platform frame and the floating frame.
Another vehicular low profile, self-propelled aerial work platform having an articulated parallelogram boom assembly is disclosed in U.S. Pat. No. 5,584,356, also owned by the Assignee of the instant application, and is hereby incorporated by reference. The articulated boom assembly includes a lower boom assembly having pairs of compression and tension arms pivotally connected between a support frame on the vehicle and a floating frame, and an upper boom assembly having pairs of compression and tension arms pivotally connected between the floating frame and a riser connected to the proximate end of a telescopic boom assembly having a work platform connected to the distal end thereof. The ends of the tension arms in the upper and lower boom assemblies, which are pivotally connected to the floating frame, share the same pivot connection so that when the articulated parallelogram is in the folded position, the tension arms are inter-digitated and lie in the same common plane so that the vehicle can be maneuvered through a low doorway, in the order of six feet, seven inches. A synchronization linkage is mounted in the floating frame and connected between the pairs of compression arms in the upper and lower boom assemblies for maintaining the floating frame in a vertical orientation during the elevating and folding of the articulated parallelogram boom assembly.
While the self propelled aerial work platforms disclosed in the aforementioned patents have been satisfactory for their intended purposes, certain features contained in these self propelled aerial work platforms are employed in the low profile self propelled aerial work platform of the present invention to provide a new combination of components; whereby the telescopic boom assembly can be folded to a lowered position so that the vehicle can be maneuvered through standard height six foot, seven inch doorways.